1. Field of the Invention
This invention relates to apparatus and a method of utilizing lasers to create shock waves in gaseous environments by ionization techniques and then using the generated power of the shock waves to pierce or cut one or more holes into a brittle material such as an electronic circuit board.
2. Description of the Prior Art
The application of lasers for cutting techniques is generally well known, and the literature is replete with numerous devices and methods. The unique beam shaping capabilities coupled with the ability to generate high power pulses have made lasers the subject of intense scrutiny for purposes as diverse as delicate eye surgery and weapons of destruction. The vast number of these investigations employ localized heating to burn away material and thereby make the necessary cut and are typified by patents such as Fry, U.S. Pat. No. 3,629,564. This heating, while advantageous in some situations, can be a detriment and in any case involves high powered lasers.
Another problem is the removal of residue resulting from the cutting operation. The use of air to sweep away the debris is shown in Houdicroft, U.S. Pat. No. 3,612,814. This patent teaches cutting a work piece with a laser beam 26 and then using a pressure differential to sweep away the debris caused by the cutting action (see Col. 2, lines 15-33). In the example described in connection with FIG. 1, the work piece is assumed to be a material such as paper, cloth or the like which is easily cut by the laser. The beam cuts cloth 32 and the low pressure in chamber 36 causes air to rush through the cut and carry away the debris. A pumping chamber 36 is used to create the low pressure.
Similarly, Konig, U.S. Pat. No. 3,649,806, teaches a method for forming perforations in a work piece and combines an energy beam, such as an electron beam or laser (see Col. 4, lines 15 et seq), and gaseous pressure for blowing out the material in the perforation. This patent is directed only to using the beam to heat the work piece to a liquid or vapor at the point to be perforated. The gaseous pressure is provided by an auxiliary substance which is typically embedded in the backing of the work piece. After initial perforation, the beam strikes the auxiliary substance and vaporizes it. The high pressure resulting from the vaporization blows the molten particles of the work piece away.
An example of the use of high power lasers is found in Saunders, U.S. Pat. No. 3,742,182 where a mask of stainless steel or other such material is placed over the sheet to be perforated and the laser is scanned, burning holes along the path in conformance with a hole pattern in the mask. A jet of air is utilized to sweep away the debris. The size of the beam is purposely focused to a larger diameter than the hole to be drilled to insure that complete burning takes place. Such applications of lasers, there a CO.sub.2 laser at 10.6 microns, indicate the object of relying on burning or vaporization of the material itself as opposed to the generation of shock waves as in the present invention which does the work on the material.